U.S. patent application number 15/616240 was filed with the patent office on 2018-01-04 for method for evenly distributing plastic melt in a hot runner system using strain gauges.
The applicant listed for this patent is IMFLUX INC.. Invention is credited to Gene Michael Altonen, Brian Matthew Burns, William Francis Lawless, III, Rick Alan Pollard.
Application Number | 20180001531 15/616240 |
Document ID | / |
Family ID | 59071126 |
Filed Date | 2018-01-04 |
United States Patent
Application |
20180001531 |
Kind Code |
A1 |
Lawless, III; William Francis ;
et al. |
January 4, 2018 |
METHOD FOR EVENLY DISTRIBUTING PLASTIC MELT IN A HOT RUNNER SYSTEM
USING STRAIN GAUGES
Abstract
A hot runner injection molding apparatus, and method of use, is
disclosed in which strain gauges are provided in the temperature
zones of the hot runner injection molding apparatus and a hot
runner controller creates a target strain profile, detects
deviations from the target strain profile in any temperature zone
based on the strain readings provided by the strain gauges in each
temperature zone, and instructs correction of deviations from the
target strain profile in any deviating temperature zone by
adjusting the heat produced by a heater or heaters in the deviating
temperature zone. The target strain profile may be based on a
median or average of strain readings provided over time by the
strain gauges in each temperature zone. A hollow installation tube
for placing the strain gauges in the hot runner injection molding
apparatus is also disclosed.
Inventors: |
Lawless, III; William Francis;
(Medford, MA) ; Pollard; Rick Alan; (Moscow,
OH) ; Altonen; Gene Michael; (Hamilton, OH) ;
Burns; Brian Matthew; (Mason, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IMFLUX INC. |
Hamilton |
OH |
US |
|
|
Family ID: |
59071126 |
Appl. No.: |
15/616240 |
Filed: |
June 7, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62356648 |
Jun 30, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 2945/76481
20130101; B29C 45/2737 20130101; B29C 45/1782 20130101; B29C
45/2738 20130101; B29C 45/77 20130101; B29C 45/78 20130101; B29C
2945/76752 20130101; B29C 2945/76274 20130101; B29C 2945/76531
20130101; B29C 2945/76759 20130101; B29C 2945/76745 20130101; B29C
2945/76103 20130101 |
International
Class: |
B29C 45/78 20060101
B29C045/78; B29C 45/27 20060101 B29C045/27 |
Claims
1. An injection molding apparatus, comprising: a mold comprising
one or more mold cavities; a ram arranged to form a shot of molten
thermoplastic material; a system nozzle arranged to inject a shot
of molten thermoplastic material through a hot runner manifold; a
plurality of hot runner nozzles adapted to receive molten
thermoplastic material from the hot runner manifold and inject the
molten thermoplastic material into a plurality of mold cavities,
each mold cavity connected to one hot runner nozzle; a plurality of
temperature zones, each temperature zone associated with one of the
plurality of mold cavities and including at least a portion of the
hot runner manifold, the associated mold cavity, and the hot runner
nozzle connected to the associated mold cavity; a plurality of
heaters, each heater connected to a hot runner controller, each
temperature zone including at least one heater; and a plurality of
strain gauges, each strain gauge in communication with the hot
runner controller and each temperature zone provided with at least
one strain gauge, wherein the hot runner control comprises a set of
a set of instructions that are stored on a non-transitory
machine-readable medium to create a target strain profile, to
detect deviations from the target strain profile in any temperature
zone based on the strain readings provided by the strain gauges in
each temperature zone, and to instruct correction of deviations
from the target strain profile in the deviating temperature zone by
adjusting the heat produced by the at least one heater in the
deviating temperature zone.
2. The injection molding apparatus of claim 1, wherein the target
strain profile is based on a median or average of strain readings
provided over time by the strain gauges in each temperature
zone.
3. The injection molding apparatus of claim 1, wherein the target
strain profile is predetermined.
4. The injection molding apparatus of claim 1, wherein the at least
one strain gauge provided for each temperature zone is located at
least one of: in the portion of the hot runner manifold associated
with the temperature zone, on an outer surface of a mold cavity
associated with the temperature zone, and in the hot runner nozzle
connected to the mold cavity associated with the temperature
zone.
5. The injection molding apparatus of claim 1, further comprising a
plurality of thermocouples, each heater associated with a
thermocouple connected to the hot runner controller.
6. The injection molding apparatus of claim 4, wherein at least one
of the at least one strain gauge provided for each temperature zone
is located in an aperture provided in the portion of the hot runner
manifold associated with the temperature zone or in the hot runner
nozzle connected to the mold cavity associated with the temperature
zone, and wherein an alternative material insert made from a
material that amplifies the strain experienced by the strain gauge
surrounds the aperture.
7. The injection molding apparatus of claim 6, wherein the
alternative material insert has a lower flex modulus than the
surrounding hot runner manifold.
8. The injection molding apparatus of claim 6, wherein the
alternative material insert is one of aluminum, brass, titanium,
thermoset plastic, composite, and steel with a lower flex modulus
than base steel or a combination of two or more of these
materials.
9. The injection molding apparatus of claim 6, wherein a minimum
distance must be maintained between a bottom or a side of the
aperture and an internal melt flow conduit wall to avoid cracking
or leaking through the internal melt flow conduit wall.
10. The injection molding apparatus of claim 9, wherein the minimum
distance is at least 0.5 mm.
11. The injection molding apparatus of claim 1, further comprising;
a hollow strain gauge installation tube connected to one of the
plurality of strain gauges; a removable insulator fitted around the
top of the hollow strain gauge installation tube; a wire channel
connected to a hollow interior of the hollow strain gauge
installation tube.
12. The injection molding apparatus of claim 11, wherein the hollow
strain gauge installation tube is connected to an extension of one
of the plurality of hot runner nozzles.
13. A method of evenly distributing molten thermoplastic material
to multiple cavities using a hot runner system in a molding
apparatus comprising: creating, by one or more processors, a target
strain profile for a molding process of a molding apparatus;
receiving, by the one or more processors, strain readings
reflecting changes in strain during a molding process as an output
from at least one strain gauge in each of a plurality of
temperature zones of the molding apparatus, monitoring, by the one
or more processors, the strain readings for each temperature zone
in order to detect a deviation from the target strain profile by a
temperature zone; if a deviation is detected, determining, by the
one or more processors, whether the deviation exceeds a deviation
limit; if the deviation exceeds a deviation limit, adjusting heat
produced by one or more heaters in the deviating temperature zone
in order to correct the deviation.
14. The method of claim 13, wherein the target strain profile is
based on a median or an average of the strain readings provided by
the plurality of temperature zones.
15. The method of claim 13, wherein the target strain profile is
predetermined.
16. The method of claim 13, wherein at least one of the at least
one strain gauge in each of the plurality of temperature zones is
located at least one of: in a portion of a hot runner manifold, on
an outer surface of a mold, and in a hot runner nozzle.
17. The method of claim 13, and amplifying the changes in strain
sensed by the at least one strain gauge in at least one of the
plurality of temperature zones using an alternative material
insert.
18. A method of installing a strain gauge in an injection molding
system comprising: connecting a hollow strain gauge installation
tube to a strain gauge that has been placed in an aperture; feeding
a wire of the strain gauge through the hollow interior of the
hollow strain gauge installation tube and into a wire channel;
turning the hollow strain gauge installation tube until the strain
gauge is tightly secured within the aperture; fitting a removable
insulator around the top of the strain gauge installation tube.
19. The method of claim 18, wherein the aperture is located in an
extension of a hot runner nozzle.
20. The method of claim 18, and inserting the hollow strain gauge
installation tube through a side of a mold.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is the non-provisional, and claims the
benefit of the filing date under 35 USC .sctn.119(e) of, U.S.
Provisional Appl. No. 62/356,648, filed Jun. 30, 2016, which is
hereby incorporated by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] This application relates generally to injection molding and,
more specifically, to a method of automatically balancing a hot
runner system in an injection molding process using strain gauge
values for a particular manifold, cavity nozzle, or temperature
control zone either on the surface of the hot runner manifold, on
the surface of the hot runner nozzle, or on the outer surface of
the mold, to correspond to an apparent melt pressure. In
particular, this application relates to identifying the difference
in apparent melt pressure for each manifold, cavity or hot runner
temperature zone during an injection molding process using
parameters sensed by at least one strain gauge and changing heat
produced by heaters in that temperature zone to equally balance the
flow of molten plastic.
BACKGROUND
[0003] At the start of an injection molding process, thermoplastic
pellets are fed by a hopper into a heated barrel and driven to the
end of the heated barrel by a reciprocating screw. The
thermoplastic pellets melt into a molten thermoplastic material,
and shots of thermoplastic material are injected through a nozzle.
The molten thermoplastic material then flows through either a cold
runner or a hot runner to the gates of each individual cavity of a
mold. After entering the gate, the molten thermoplastic material
fills a mold cavity formed between two or more sides of the mold
held together under pressure by a press or clamping unit. Once the
shot of molten thermoplastic material is injected into the mold
cavity, the reciprocating screw stops traveling forward. The molten
thermoplastic material takes the form of the mold cavity and cools
inside the mold until it solidifies. Then the clamping unit
releases the mold sides and the finished part is ejected from the
mold.
[0004] The injection molding process may incorporate molds which
manufacture multiple parts for each representative cycle, each of
the multiple parts being formed in a distinct mold cavity. The mold
may be identified by the number of parts that it manufactures in
each cycle. For example, if a mold manufactures eight parts at a
time, it is referred to as an eight-cavity mold. The runner system
of a mold includes channels which deliver plastic to each
individual cavity. A runner system is referred to a cold runner
system or a hot runner system.
[0005] Whatever the particular cavitation of a mold, or type of
runner system, distributing the molten plastic evenly to each
individual cavity is desirable in order to prevent some cavities
from filling too soon or too late, or at too high a pressure or too
low a pressure, as this would have a potential effect on the
quality for the parts produced. Specifically, the flow of plastic
to a particular cavity could occur before or after the overall
average fill time of the group, resulting in inconsistent quality
of parts. For example, if cavity 1 fills first or at a higher
pressure, followed by cavities 2-7 filling simultaneously or at
median pressure, followed by cavity 8 filling lastly or at a lower
pressure, the part formed in cavity 1 may have a defect known as
flash or may be heavier or dimensionally larger part than the parts
produced in cavities 2-8 Likewise, the part formed in cavity 8 may
have a defect known as a short-fill or may be a lighter or
dimensionally smaller part than the parts produced in cavities
1-7.
[0006] A cold runner system is a method of delivering plastic to
each cavity of a mold in which plastic cools and solidifies into
the shape of the desired part as defined by the mold cavity and
into the shape of the channels that were designed to distribute the
plastic melt to each mold cavity. The cold runner system is
geometrically designed to account for the flow lengths and pressure
drops to each gate location for each mold cavity in order to
balance the fill of each mold cavity as equally as possible.
However, the plastic from the runner system needs to be discarded
as either scrap or needs to go through an additional process of
being recycled (regrind) and re-introduced to the molding process
at another time. This adds an overall increase in cost to produce
any given plastic part using a cold runner system.
[0007] A hot runner system, similar to a cold runner system, is
geometrically designed to account for the flow lengths and pressure
drops to each gate location for each mold cavity. In addition, hot
runners are thermally designed with heating zones which may be
controlled with a heater and thermocouple combination to keep the
plastic within its channels molten so that it may be used
immediately for the next cycle. This eliminates the scrap and
regrind that are associated with a cold runner system. Although hot
runners are geometrically and thermally designed to distribute the
flow of plastic evenly to each cavity of the mold, the effects of
differential of heat transfer throughout the hot runner system as
well as variation of melt due to laminar flow effects often
necessitate changing temperatures in the hot runner system through
trial and error. The change in temperatures is routinely
accomplished using an output such as part weight or part dimension
to determine which zones need to be changed in order to achieve
optimal balance of fill to each cavity.
[0008] Ideally, sensors for monitoring an injection molding process
would be indirect, easy to install, and inexpensive. Direct
sensors, such as sensors placed within a mold cavity, leave
undesirable marks on part surfaces. For example, while demand for
injection molded parts with high gloss finishes has been
increasing, direct sensors positioned in the mold cavity have a
tendency to mar the high gloss finish of the parts, requiring
post-molding operations to machine or otherwise mask or remove the
marred regions from the parts. As a result, indirect sensors that
are not located in the mold cavity are preferable. Additionally,
when the molding system is being used to make products for medical
applications, contact between a sensor and the thermoplastic
material may be prohibited.
[0009] More recently, strain gauges have been placed on a mold
surface, within a nozzle adapter, or elsewhere within an injection
molding apparatus, in order to measure how strain at the measured
location changes over the course of a standard injection molding
process. For example, a strain gauge sensor placed on the exterior
of the mold surface adjacent to a parting line of a mold, as
described in co-owned U.S. Patent Application No. 62/303,654,
"External Sensor Kit for Injection Molding Apparatus and Methods of
Use," the entirety of which is hereby incorporated by reference, is
able to sense the surface strain changes on the mold surface that
occur over time as a result of the closing and opening forces. In
response to surface strain changes, the strain gauge sensor emits
an electrical signal, typically in the range of -10 to 10 Volts.
The signal emitted by the strain gauge sensor is received and used
by a controller to approximate one or more conditions within the
mold, such as the pressure within the mold cavity or the location
of the melt flow front. In certain molds in which the ratio of the
length of the flow channel to the thickness of the molded part is
great, i.e. molds having a high length-to-thickness (L/t) ratio,
the pressure at the melt flow front may be approximated based on
the signals emitted by the strain gauge sensor(s).
SUMMARY
[0010] Embodiments within the scope of the present disclosure are
directed to methods of thermally balancing a hot runner system of
an injection molding process using sensed parameters provided by an
external sensor. Strain gauge sensors are the type of sensor
primarily discussed, while other sensors capable of detecting
movement of steel as a proxy or tell-tale for internal conditions
such as melt pressure, could achieve the same purpose as a strain
gauge sensor and are within the scope of the present disclosure.
For example, microwave sensor kits, x-ray sensor kits, ultrasonic
sensor kits, air pressure sensor kits, air temperature sensor kits,
and sub-surface temperature sensor kits, could all be substituted
for the strain gauge sensors described and depicted below.
Additionally, other types of external gauge sensors, such as
electrical, electronic, mechanical, wireless, and fiber optic
sensors, could be utilized instead of strain gauge sensors. Strain
gauge sensors located on mold surfaces, hot runner manifold
surfaces, and hot runner nozzle surfaces are primarily discussed
below, while strain gauge sensors located in other locations within
an injection molding apparatus could achieve the same purposes.
[0011] Throughout an injection molding process, the hot runner
system and the outer steel plates of the mold experience changes in
strain. The strain experienced by a hot runner system or the outer
steel plates of a mold may differ depending on what type of
injection molding process is being used. Strain gauges or pins
located on mold surfaces, hot runner manifold surfaces, or hot
runner nozzle surfaces are able to sense changes in strain and
provide strain change data to a controller. The controller may
contain a strain profile that has been developed to identify target
strain values and times to reach the target strain values. The
target strain profile can be compared to sensed strain values over
time for each quadrant, nozzle cavity, or hot runner temperature
zone during an injection molding process. The target strain profile
may be based on a median or average value of strain value over time
for all of the cavities being compared.
[0012] Hot runner temperature zones can be balanced by changing the
temperature set point for a particular zone that exhibits a strain
profile that occurs sooner or later, or exhibits a greater or
lesser change in strain, than the target strain profile indicates
should be the case. For example, if a first cavity in an eight
cavity mold experiences a peak strain prior to the time when the
target strain profile suggests the peak strain should be
experienced but the other seven cavities are following the target
strain profile, plastic is flowing more easily into the first
cavity than into the second through eighth cavities. The controller
can identify this deviation from the target strain profile using an
algorithm, can determine whether the deviation from the target
strain profile exceeds an acceptable deviation limit, and can, if
necessary, calculate how much the temperature in the temperature
zone for the first cavity should be decreased in order to correct
the deviation. The controller can then, via a connector and
thermocouple, reduce the heat being generated by the heaters in the
temperature zone for the first cavity accordingly.
[0013] Strain gauges or pins that are installed on a hot runner
manifold or hot runner nozzle are potentially more accurate than
using a strain gauge installed on the outer surfaces of the steel
plates on the outside of the mold. However, the cost in
installation or removal could be in systems in which the mold
plates have to be disassembled in order to access the strain
gauges/pins for installation or removal. To avoid this increase in
cost, component assemblies for hot runner injection molding systems
may be designed to allow for the installation and removal of strain
gauges/pins without disassembly and reassembly of the mold plates.
For example, a strain gauge installation tube may be used to allow
for both the protection and insulation of the strain gauge or pin
cable. The strain gauge installation tube may also act as an
extension tool in order to install the strain gauge/pin to the
specified torque, as well as loosen and remove the strain gauge/pin
without disassembly or reassembly of the mold plates. Likewise, the
hot runner nozzle may be design to include an area of steel which
would be offset so that installation or removal of a strain
gauge/pin could be performed without disassembly or reassembly of
the mold plates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter that is
regarded as the present disclosure, it is believed that the
disclosure will be more fully understood from the following
description taken in conjunction with the accompanying drawings.
Some of the figures may have been simplified by the omission of
selected elements for the purpose of more clearly showing other
elements. Such omissions of elements in some figures are not
necessarily indicative of the presence or absence of particular
elements in any of the exemplary embodiments, except as may be
explicitly delineated in the corresponding written description.
None of the drawings are necessarily to scale.
[0015] FIG. 1 illustrates, semi-schematically, a conventional
injection molding apparatus, wherein a hot runner system comprised
of a hot runner manifold system with hot runner nozzles leading to
mold cavities formed by mold plates is equipped with strain
gauges/pins on either the hot runner manifolds, the hot runner
nozzles, the outer surface of the mold plates, or a combination
thereof.
[0016] FIG. 1A illustrates an enlarged cross-sectional view of the
strain pin installed on the hot runner manifold depicted in FIG.
1.
[0017] FIG. 1B illustrates an enlarged cross-sectional view of the
strain pin installed on the hot runner nozzle depicted in FIG.
1.
[0018] FIG. 2 illustrates an exemplary target strain profile for
the displaying the comparison of median strain value target and
median target time to reach strain value target for cavities
1-8.
[0019] FIG. 3 illustrates a top view of four hot runner manifolds
in an eight-cavity molding apparatus, each hot runner manifold
leading to two molds and containing two strain pins.
[0020] FIG. 4 illustrates a top view of the nozzles of an
eight-cavity molding apparatus, each nozzle containing a strain
pin.
[0021] FIG. 5 illustrates a top view of an eight-cavity mold having
eight strain gauges, one for each cavity, placed on the side of the
mold.
[0022] FIG. 6 illustrates a strain gauge installation tube used for
installation or removal of a strain gauge in a hot runner
manifold.
[0023] FIG. 7 illustrates a strain gauge installation tube used for
installation or removal of a strain gauge in a hot runner
nozzle.
[0024] FIG. 8 is a schematic illustration of a hot runner
controller for an injection molding system.
DETAILED DESCRIPTION OF THE INVENTION
[0025] Referring to the figures in detail, FIG. 1 illustrates an
exemplary injection molding apparatus 10 for producing
thermoplastic parts in high volumes (e.g., a class 101 injection
mold, or an "ultra-high productivity mold", a class 102
(medium-to-high productivity mold), or class 103 (a medium
productivity mold)). The injection molding apparatus 10 generally
includes an injection system 12 and a clamping system 14. A
thermoplastic material may be introduced to the injection system 12
in the form of thermoplastic pellets 16. The thermoplastic pellets
16 may be placed into a hopper 18, which feeds the thermoplastic
pellets 16 into a heated barrel 20 of the injection system 12. The
thermoplastic pellets 16, after being fed into the heated barrel
20, may be driven to the end of the heated barrel 20 by a ram, such
as a reciprocating screw 22. The heating of the heated barrel 20
and the compression of the thermoplastic pellets 16 by the
reciprocating screw 22 causes the thermoplastic pellets 16 to melt,
forming a molten thermoplastic material 24. The molten
thermoplastic material is typically processed at a temperature of
about 130.degree. C. to about 410.degree. C.
[0026] The reciprocating screw 22 forces the molten thermoplastic
material 24 toward a nozzle 26 to form a shot of thermoplastic
material, which will be injected into a sprue or inlet 71. The
temperature of inlet 71 is maintained by an inlet heater 72 and
inlet thermocouple 73. The molten material 24 flows through
crossover manifold 74, which is maintained at a desired temperature
by crossover heater 75 and crossover thermocouple 75. The molten
material 24 then flows to one or more manifolds 77 maintained at a
desired temperature by a manifold heater 78 and a manifold
thermocouple 79. The molten material 24 then flows to one or more
hot runner nozzles 80 maintained at a desired temperature by a
nozzle heater 81 and a nozzle thermocouple 82. The molten
thermoplastic material 24 may be injected through a gate 30, which
directs the flow of the molten thermoplastic material 24 to the
mold cavity 32. The mold cavity 32 is formed between first and
second mold sides 25, 27 of the mold 28 and the first and second
mold sides 25, 27 are held together under pressure by a press or
clamping unit 34. The press or clamping unit 34 applies a clamping
force during the molding process that is greater than the force
exerted by the injection pressure acting to separate the two mold
halves 25, 27, thereby holding the first and second mold sides 25,
27 together while the molten thermoplastic material 24 is injected
into the mold cavity 32. In a typical high variable pressure
injection molding machine, the press typically exerts 30,000 psi or
more because the clamping force is directly related to injection
pressure. To support these clamping forces, the clamping system 14
may include a mold frame and a mold base.
[0027] Once the shot of molten thermoplastic material 24 is
injected into the mold cavity 32, the reciprocating screw 22 stops
traveling forward. The molten thermoplastic material 24 takes the
form of the mold cavity 32 and the molten thermoplastic material 24
cools inside the mold 28 until the thermoplastic material 24
solidifies. Once the thermoplastic material 24 has solidified, the
press 34 releases the first and second mold sides 25, 27, the first
and second mold sides 25, 27 are separated from one another, and
the finished part may be ejected from the mold 28. The mold 28 may
include a plurality of mold cavities 32 to increase overall
production rates. The shapes of the cavities of the plurality of
mold cavities may be identical, similar or different from each
other. The latter may be considered a family of mold cavities
32.
[0028] The embodiment depicted in FIG. 1 depicts three separate
locations that strain gauges are located. A strain gauge 100 is
provided in the hot runner manifold 77, a strain gauge 52 is
provided on the exterior of the mold 28, and a strain gauge 83 is
provided in a hot runner nozzle 80. Additional detail is provided
in FIGS. 1A and 1B regarding placement of strain gauges 100 and 83.
Strain gauge 52 may be placed on the exterior of the mold directly
or using a coupon, as described in co-owned U.S. Patent Application
No. 62/303,654, "External Sensor Kit for Injection Molding
Apparatus and Methods of Use," incorporated herein by reference.
The strain gauges 100, 52, and 83 are in communication with a hot
runner controller 91 via strain gauge connector 86. Strain gauges
100, 52, and 83 may be strain pins or any type of strain measuring
mechanism. In some embodiments within the scope of the present
disclosure, only one or two of strain gauges 100, 52, and 83 are
provided.
[0029] The hot runner controller 91 is in communication with inlet
thermocouple 73, crossover thermocouple 76, manifold thermocouple
79, and nozzle thermocouple 82 via thermocouple connector 85. The
hot runner controller 91 is in further communication with inlet
heater 72, crossover heater 75, manifold heater 78, and nozzle
heater 81 via heater connector 84. The temperature of each heating
zone is maintained at a set point by an algorithm, which determines
if the thermocouple reading of measured temperature taken by
thermocouple 76, 79, or 82 matches a set point value for the
corresponding zone.
[0030] The hot runner controller 91 maintains a balance in
temperature throughout the hot runner manifold 77 to prevent
defects in the parts made in mold cavities 32. To achieve this end,
the strain gauge values communicated by the strain gauge connector
86 are compared to a target strain profile for the set point
temperature of the manifold heater 78 or nozzle heater 81, and the
temperature produced by the manifold heater 78 or the nozzle heater
81 may be increased or decreased depending on what is necessary to
correct any impermissible deviation from the target strain profile.
The target strain profile may be predetermined. The predetermined
target strain profile may be based upon historical strain process
information, such a historical median or average of strain value
over time for all of the cavities being filled. Alternately, the
target strain profile may be determined as an injection molding
process is occurring based upon the median or average value of
strain value over time for all of the cavities being filled. The
hot runner controller 91 may include a microprocessor (or another
suitable processing unit, or several such units), a non-transitory
memory, and one or more communication links.
[0031] In FIG. 1A, an enlarged cross-sectional view of the manifold
77 shows the path of molten thermoplastic material 24. A strain
gauge aperture 104 is provided in an external wall 106 of the
manifold 77 to accommodate strain gauge 100. In some embodiments,
the longitudinal axis of strain gauge aperture 104 is perpendicular
to the axis of the melt flow conduit 102. A minimum distance 108
must be maintained between the bottom 110 of the strain gauge
aperture 104 and an internal melt flow conduit wall 112 to avoid
cracking or leaking through the internal melt flow conduit wall
112. In some embodiments within the scope of the present
disclosure, the minimum distance 108 is 0.5 mm.
[0032] In some embodiments within the scope of the present
disclosure, the strain gauge aperture 104 may be formed in an
alternative material insert 114 that is made of a different
material than the rest of the hot runner manifold 77. In some
embodiments, the hot runner manifold 77 is made from stainless,
pre-treated steel while the alternative material insert 114 is made
from aluminum, brass, titanium, thermoset plastic, composite, and
steel with a lower flex modulus than base steel or a combination of
two or more of these materials. steel with a lower flex modulus
than base steel, or another material that will better amplify the
strain for detecting by the strain gauge pin 83. The alternative
material insert 114 may have a lower flex modulus than the material
of the rest of the hot runner manifold 77. In some embodiments, the
alternative metal insert is formed from a modified metallurgy that
expands at the same rate as steel. The minimum distance 108 may
vary depending upon the material forming the alternative material
insert 114.
[0033] In FIG. 1B, an enlarged cross-sectional view of a hot runner
nozzle 80 shows the path of molten thermoplastic material 24
through the hot runner nozzle 80. A cylindrical nozzle heater 81 is
provided around the hot runner nozzle 80 and a nozzle thermocouple
82 is provided near the cylindrical nozzle heater 81. Two strain
gauges 83 are provided in strain gauge apertures 116 and 118
respectively on external walls 120 and 121 respectively. Minimum
distance 122 must be maintained between the side of strain gauge
aperture 116 and an internal melt flow conduit wall 124, and
minimum distance 126 must be maintained between the bottom of
strain gauge aperture 118 and the internal melt flow conduit wall
124 to avoid cracking or leaking through the internal melt flow
conduit wall 124. In some embodiments within the scope of the
present disclosure, the minimum distance 108 is 0.5 mm.
[0034] In some embodiments within the scope of the present
disclosure, the strain gauge apertures 116 and 118 may be formed in
an alternative material inserts 128 and 130 respectively. The
alternative material inserts 128 and 130 are made from a different
material than the rest of the hot runner nozzle 80. The alternative
material inserts 128 and 130 may be made from the same or a
different material from one another. The alternative material
inserts 128 and 130 may have a lower flex modulus than the material
of the rest of the hot runner nozzle 80. In some embodiments, the
hot runner nozzle 80 is made from stainless, pre-treated steel
while the alternative material inserts 128 and 130 are made from
one of aluminum, brass, titanium, thermoset plastic, composite, and
steel with a lower flex modulus than base steel or a combination of
two or more of these materials. that will better amplify the strain
for detecting by the strain gauge pins 83. In some embodiments, the
alternative metal insert is formed from a modified metallurgy that
expands at the same rate as steel. The minimum distances 122 and
126 may vary depending upon the material forming the alternative
material insert 114.
[0035] FIG. 2 illustrates an exemplary comparison of the target
strain profile 93 for a molding cycle of an eight-cavity mold. A
target peak strain 132 is identified on the target strain profile
93 at target peak strain time 92. The target strain profile 93
represents the median of strain readings obtained by strain gauges
52, 100, or 83, or a combination thereof, at temperature zones for
the second through eighth cavities of the eight-cavity mold, and
provided by strain gauge connector 86 to the hot runner controller
91. A strain profile 134 generated by the hot runner controller 91
from strain readings received through strain gauge connector 86
from a strain gauge 52, 100, or 83 or a combination thereof, is
also provided for a first cavity of the eight-cavity mold. The
strain profile 132 achieves a peak strain 135 at a time 136
occurring before target peak strain time 92. An algorithm of the
controller 91 can identify the deviation of first cavity strain
profile 134 from the target peak strain profile 93 and take
corrective action, such as instructing thermocouple 79, 76, 79, and
82 via thermocouple connector 85 to adjust the heat produced in the
temperature zone for the first cavity by heaters 72, 75, 78, and 81
respectively. As the temperature in the temperature zone for the
first cavity changes, the deviation of the first cavity strain
profile 134 from the target strain profile 93 is eliminated.
[0036] FIGS. 3-5 depict possible locations to install the strain
gauges 100, 83, and 52 respectively. FIG. 3 depicts four hot runner
manifolds 77a, 77b, 77c, 77d, each hot runner manifold 77a-77d
receiving molten thermoplastic material 24 from a primary melt flow
conduit 200 and distributing molten thermoplastic material to a
secondary melt flow conduit 202 that connects to two mold cavities
32. Each hot runner manifold 77a-77d includes two strain pins 100,
such that a strain pin 100 is associated with each mold cavity 32.
In hot runner manifold 77a, strain pins 100 are installed to the
side of secondary melt flow conduit 201. In hot runner manifold
77b, strain pins 100 are installed above secondary melt flow
conduit 202. In other embodiments within the scope of the
disclosure, strain pins 100 may be installed below secondary melt
flow conduit 202 or above, to the side, or below primary melt flow
conduit 200. In some embodiments within the scope of the present
disclosure, more than one strain pin 100 may be associated with
each mold cavity 32. In other embodiments within the scope of the
present disclosure, hot runner manifolds 77a-77d may include only
one mold cavity 32 or may include more than 2 mold cavities 32. The
number of conduits through which molten thermoplastic material 24
travels in order to reach the hot runner manifolds 77a-77d may
vary, the number of conduits through which molten thermoplastic
material 24 travels in the hot runner manifolds 77a-77d to reach
mold cavities 32 may vary, and the number of hot runner manifolds
in an injection molding apparatus 10 may vary.
[0037] FIG. 4 depicts eight hot runner nozzles 80, each hot runner
nozzle 80 connected to a mold cavity 32 (not pictured). A strain
gauge 83 is installed in each hot runner nozzle 80. In four hot
runner nozzles 80, the strain gauge 83 is installed on a side 80a
of the hot runner nozzle 80 that is closest to other hot runner
nozzles 80. In the other four hot runner nozzles 80, the strain
gauge 83 is installed on a side 80b of the hot runner nozzle 80
that is farther from the other hot runner nozzles 80. In some
embodiments within the scope of the present disclosure, more than
one strain pin may be associated with each hot runner nozzle
80.
[0038] FIG. 5 depicts hot runner nozzles 90 attached to a mold side
25, and eight strain gauges 52 are attached to the outside of the
mold side 25. One mold cavity 32 (not pictured) is associated with
each strain gauge 52. In some embodiments within the scope of the
present disclosure, more than one strain pin may be associated with
each mold cavity 32. Additionally, the strain gauges 52 may be
placed on other surfaces of a mold 28 in other embodiments within
the scope of the present disclosure.
[0039] FIG. 6 exhibits a method to install a strain pin 100 in a
hot runner manifold 77 using a hollow strain gauge installation
tube 92. In some embodiments within the scope of the present
disclosure, the male hex fitting 100a of the strain pin 100 is
turned clockwise or counterclockwise with the female hex fitting
92a of the strain gauge installation tube 92 which is driven by
using a wrench or socket to turn the strain gauge installation tube
92 clockwise or counterclockwise by a male hex fitting 92b or
female hex fitting 92c at the top of the hollow strain gauge
installation tube 92. In other embodiments within the scope of the
present disclosure, the hollow strain gauge installation tube 92
will have other mechanisms or designs known in the art for
connection with a wrench, socket, or other installation tool. The
strain gauge installation tube 92 is hollow, which allows the
strain pin wire 100b to be fed through the strain gauge
installation tube 92, then through the slot 92d for the strain pin
wire 100b and into the wire channel 94. After installation of the
strain pin 100, a removable insulator 93 is fitted around the top
of the strain gauge installation tube 92 to provide thermal
isolation and keep the strain gauge installation tube 92 from
moving. The removable insulator 93 may be made from a thermoset
plastic material or a thermoplastic material with a continuous use
temperature above 200.degree. F.
[0040] FIG. 7 illustrates a nozzle 80 modified with an extension 95
so that a strain pin 83 can be installed in the same manner
depicted in FIG. 6. The strain gauge installation tube 92 passes
through mold side 25 to reach extension 95 of the nozzle 80. The
removable insulator 93 is fitted around the top of the strain gauge
installation tube 92 in the mold side 25, and the wire channel 94
is provided in the mold side 25. In other embodiments within the
scope of the present disclosure, the strain gauge installation tube
92 may pass through mold side 27 or any other region of a mold 28,
through hot runner manifold 77, or through any area suitable area
of the injection molding apparatus 10.
[0041] FIG. 8 illustrates a block diagram of an example hot runner
controller 300 (such as hot runner controller 91) that may be
utilized in an injection molding system. The virtual cavity sensor
300 may include, for example, one more central processing units
(CPUs) or processors 302, and one or more busses or hubs 304 that
connect the processor(s) 302 to other elements of the virtual
cavity sensor 300, such as a volatile memory 306, a non-volatile
memory 308, a display controller 310, and an I/O interface 312. The
display controller 310 may be connected to a display 314. The
volatile memory 306 and the non-volatile memory 308 may each
include one or more non-transitory, tangible computer readable
storage media such as random access memory (RAM), read only memory
(ROM), FLASH memory, a biological memory, a hard disk drive, a
digital versatile disk (DVD) disk drive, etc.
[0042] In an embodiment, the memory 306 and/or the memory 308 may
store instructions 312 that are executable by the processor 302.
For example, in a molding apparatus particularly configured to
perform the techniques described herein, the instructions may be
the instructions executed by the controller 300. In these
embodiments, the instructions stored in the memories 306 and 308
may also include instructions to perform the actions described with
respect to the controller.
[0043] The controller 300 is only one example of a controller
suitable to be particularly configured for use in a molding
apparatus. Other embodiments of the controller 300 may also be
particularly configured for use in a molding apparatus, even if the
other embodiments have additional, fewer, or alternative components
than shown in FIG. 8, have one or more combined components, or have
a different configuration or arrangement of the components.
Moreover, the various components shown in FIG. 8 can be implemented
in hardware, a processor executing software instructions, or a
combination of both hardware and a processor executing software
instructions, including one or more signal processing and/or
application specific integrated circuits.
[0044] The dimensions and values disclosed herein are not to be
understood as being strictly limited to the exact numerical values
recited. Instead, unless otherwise specified, each such dimension
is intended to mean both the recited value and a functionally
equivalent range surrounding that value. For example, a dimension
disclosed as "40 mm" is intended to mean "about 40 mm."
[0045] Every document cited herein, including any cross referenced
or related patent or application and any patent application or
patent to which this application claims priority or benefit
thereof, is hereby incorporated herein by reference in its entirety
unless expressly excluded or otherwise limited. The citation of any
document is not an admission that it is prior art with respect to
any invention disclosed or claimed herein or that it alone, or in
any combination with any other reference or references, teaches,
suggests or discloses any such invention. Further, to the extent
that any meaning or definition of a term in this document conflicts
with any meaning or definition of the same term in a document
incorporated by reference, the meaning or definition assigned to
that term in this document shall govern.
[0046] While particular embodiments of the present invention have
been illustrated and described, it would be obvious to those
skilled in the art that various other changes and modifications can
be made without departing from the spirit and scope of the
invention. It is therefore intended to cover in the appended claims
all such changes and modifications that are within the scope of
this invention.
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